Electronic watermark insertion device, detection device, and method

ABSTRACT

The use of the undefined low-order four bits of an 8-bit watermark is defined and, when contents are reproduced, a predetermined operation is performed according to the information stored in the low-order four bits. That is, a watermark is added to an original image to create an image with the watermark inserted. When the contents are reproduced, the watermark is detected in the image and, based on the information stored in the low-order four bits of the detected watermark, a predetermined operation, for example, access to a web site on the Internet, is performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital image, and more particularlyto a device that inserts identification data, which has specialinformation, into a digital image and a device that detects theidentification data.

2. Description of the Related Art

Recently, more and more data recorded on media is digitized. On theother hand, an illegal copy of data, brought by data digitization, hasbecome a serious social problem. Electronic watermark (hereinaftercalled a watermark) insertion and detection technology, designed forpreventing illegal copies, is now being studied for practical use.Watermark technology, a technology for embedding a sort of invisible IDinformation as a noise, is characterized in that embedded informationthat constantly coexists with contents cannot be erased or modifiedeasily. Taking advantage of these characteristics, watermarkinsertion/detection technology prevents contents, such as video data,from being illegally copied.

As an example of electronic watermark technology, a method for embeddinga watermark is proposed in which, after an image is frequency-converted,the watermark is embedded into an area where the frequency of videosignal components is high. Because a watermark is embedded into ahigh-frequency component area in this method, the watermark will not beremoved even if image processing, such as compression/decompression andfiltering, is performed. The watermark embedded in this way is removedonly when the original image is destroyed. In addition, arrangingwatermarks based on random numbers generated according to normaldistribution avoids interference among watermarks, preventing imagequality from being degraded.

This method embeds a watermark in the following steps. First, theoriginal image is converted to frequency components using, for example,DCT (discrete cosine transform), and n data pieces, f(1), f(2), . . . ,f(n), each high in the frequency region, are selected. Then, watermarks,w(1), w(2), . . . ,w(n) are selected from those arranged according tonormal distribution (average is 0, covariance is 1) and, for each i, thefollowing calculation is executed.F(i)=f(i)+α×|f(i)|×w(i)where, α is a scaling element.

Then, performing inverse DCT for F(i) gives an image in which awatermark is embedded.

This method detects a watermark in the following steps. This methodrequires that the original image f(i) and a watermark candidate w(i)(where, i=1, 2, . . . , n) be known.

First, an image with a watermark embedded is converted to frequencycomponents using DCT. Let F(1), F(2), . . . , F(n) be the values ofelements corresponding to f(1), f(2), . . . , f(n) each of which has awatermark embedded in the frequency region. A watermark W(i) iscalculated and extracted using f(i) and F(i) as follows:W(i)=(F(i)−f(i))/f(i)

Next, the statistical similarity between w(i) and W(i) is calculatedusing the inner product of the vector as follows:C=W w(WD×wD)where,W=(W(1), W(2), . . . , W(n)),w=(w(1), w(2), . . . , w(n)),

WD is the absolute value of vector W, wD is the absolute value of vectorw, and is the inner product of the vector. When the statisticalsimilarity C is a value equal to or larger than a specific value, it isjudged that the watermark is embedded.

If a watermark is embedded in this method, the copyright holder of theoriginal image may find the source of digital image data that isillegally copied. This method, which requires an original image, allowsthe copyright holder to detect a watermark only when he or she has theoriginal image of image data which is thought to be copied illegally.However, on a terminal reproducer where the original image is notavailable, this method cannot be used to detect a watermark.

To solve this problem, a method improved for use on a terminal,especially for use in an MPEG system, is proposed. This method dividesthe original image into 8×8 pixel blocks and embeds and extracts awatermark into and from those blocks, one block at a time.

This method embeds a watermark in the following steps. First, let f(1),f(2), . . . , f(n) be the frequency components in the frequency region,arranged in AC frequency ascending order, for which discrete cosinetransfer has been performed during MPEG compression. Then, watermarksw(1), w(2), . . . , w(n) are selected from those arranged according tonormal distribution (average is 0, covariance is 1) and, for each i, thefollowing calculation is executed,F(i)=f(i)+α×avg(f(i))×w(i)where, α is a scaling element, and avg(f(i)) is a partial average of theabsolute values in three points near f(i).

Then, processing that follows MPEG processing is performed using F(i)instead of f(i).

This method detects a watermark in the following steps. This method doesnot require the original image; only the watermark candidates w(i)(where, i=1, 2, . . . , n) need be known.

First, let F(1), F(2), . . . , F(n) be the frequency components in thefrequency region, arranged in frequency ascending order, for whichde-quantization has been performed during MPEG decompression. With theabsolute value of the average of three points near F(i), that is,F(i−1), F(i), and F(i+1), as the partial average avg(F(i)), watermarkW(i) is calculated from W(i)=F(i)/avg(F(i)) and, for each i, the totalWF(i) of W(i) for one image is calculated.

Then, the statistical similarity of w(i) and WF(i) is calculated fromC=WF w/(WFD×wD) using the inner product of the vector. When thestatistical similarity C is a value equal to or larger than a specificvalue, it is judged that the watermark is embedded.

FIG. 8 shows the configuration of a device that inserts an electronicwatermark into MPEG-compressed image data. In the figure, numeral 802indicates a DCT transformer that performs DCT (discrete cosine)transformation for an original image 801 and outputs DCT-transformeddata, numeral 803 indicates a watermark inserter that puts watermarkweighs on the DCT coefficients as described above, numeral 804 indicatesa quantizer that quantizes the DCT coefficients into which a watermarkis inserted, numeral 805 indicates a de-quantizer that de-quantizesquantized data, numeral 806 indicates an IDCT transformer that performsIDCT(inverse discrete cosine transform) for de-quantized data, numeral807 indicates an image into which a watermark is inserted, numeral 808indicates a Huffman encoder that performs Huffman coding to compressquantized data, and numeral 809 indicates data compressed throughHuffman encoding. The device with this configuration inserts a watermarkinto the original image 801 and then provides general users with thecompressed data 809 into which a watermark is inserted.

FIG. 9 shows the configuration of a device that decodes the contentsinto which a watermark is inserted. In the figure, numeral 902 indicatesa decoder that decodes compressed data 901 into which a watermark isinserted, numeral 903 indicates an IDCT transformer that performs IDCTfor decoded data, and numeral 904 indicates a watermark detector thatdetects a watermark in data for which IDCT has been performed asdescribed above. The device with this configuration detects a watermarkinserted in the contents.

On the other hand, the configuration of a watermark is shown in FIG. 10.The high-order four bits of an eight-bit watermark contains informationdefined by the electronic watermark promotion organization. Morespecifically, the high-order two bits are defined as the CCI (copyprotection) bits and bits 3–4 are reserved. The low-order four bits areundefined.

The use of only the high-order four bits are defined with the low-orderfour bits undefined as described above. How to use the remaininglow-order four bits, reserved for future use, is a problem.

SUMMARY OF THE INVENTION

Object of the Invention

Accordingly, it is an object of the present invention to provide anelectronic watermark insertion/detection device that efficiently usesthe low-order four bits included but not defined in a watermark.

The present invention is characterized in that the undefined low-orderfour bits of an 8-bit watermark are defined for specific use and inthat, at contents reproduction time, a predetermined operation isperformed based on the information included in the low-order four bits.That is, as shown in FIG. 1, the device according to the presentinvention embeds a watermark 102 into an original image 101 to create animage in which the watermark is inserted. At contents reproduction time,the device detects the watermark included in the image and performs apredetermined operation based on the information stored in the low-orderfour bits of the detected watermark.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the concept of the present invention.

FIG. 2 is a block diagram showing an embodiment of an electronicwatermark insertion device according to the present invention.

FIG. 3 is a block diagram showing an embodiment of an electronicwatermark detection device according to the present invention.

FIG. 4 is a block diagram showing a system to which the electronicwatermark detection device according to the present invention isapplied.

FIG. 5 is a block diagram showing the embodiment of the presentinvention.

FIG. 6 is a block diagram showing the embodiment of the presentinvention.

FIG. 7 is a block diagram showing the embodiment of the presentinvention.

FIG. 8 is a block diagram showing a conventional electronic watermarkinsertion device.

FIG. 9 is a block diagram showing a conventional electronic watermarkdetection device.

FIG. 10 is a diagram showing the configuration of a conventionalwatermark.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a watermark insertion/detection device according to thepresent invention will be described with reference to the attacheddrawings.

FIG. 2 is a block diagram showing a watermark insertion device. Thiswatermark insertion device differs from a prior-art device shown in FIG.8 in that predetermined information is saved in a table file 210.

On the other hand, FIG. 3 is a block diagram showing a watermarkdetection device. This watermark detection device differs from aprior-art device shown in FIG. 9 in that, after the watermark isdetected, processing is performed according to the detected watermark.

The operation of the present invention will be described below.

First, FIG. 5 shows an example of character information displayed basedon the low-order four bits of the watermark.

In the figure, numeral 501 indicates digital contents. The digitalcontents contain image data into which the watermark is inserted as wellas a table file 505 defining the low-order four bits of the watermark.Numeral 502 indicates a computer that reproduces the digital contentsand detects the watermark. Numeral 503 indicates a reproduction screenon which reproduced image data is displayed. Numeral 504 indicates ascreen on which character information is displayed.

The computer 502 reads image data and the table file 505 from arecording medium on which digital contents are recorded. Next, thecomputer 502 reproduces the image data and displays it on thereproduction screen 503. In parallel with this operation, the computer502 extracts a watermark from the image data that was read, compares thelow-order four bits of the watermark with the information defined in thetable file 505 and, based on the comparison result, performs apredetermined operation. For example, when the low-order four bits are[0000], the computer does not display data on the screen 504. When thelow-order four bits are [0001], the computer displays the advertisementof company A on the screen 504. When the low-order four bits are [0010],the computer displays the advertisement of company B. Note thatadvertisement data that is displayed is pre-stored in the digitalcontents 501 or in the computer 502.

Next, FIG. 6 shows an example of how to access a web site on theInternet based on the low-order four bits on a watermark. In thisexample, the table file contains URLs used to access web sites on theInternet. Numeral 605 indicates a screen on which a reproduced image isdisplayed. Numeral 606 indicates a screen on which the web page of anaccessed web site is displayed.

A personal computer 604 reproduces digital contents 603. In parallelwith this operation, the computer 603 extracts a watermark, compares thelow-order four bits of the watermark with the information defined in thetable file 607 and, based on the comparison result, performs apredetermined operation. For example, when the low-order four bits ofthe watermark are [0000], the computer does not display data on thescreen 606. When the low-order four bits are [0001], the computerautomatically accesses [http://abc] and displays the contents of the webpage on the screen 606. When the low-order four bits are [0010], thecomputer accesses [http://def] and displays the contents of the web pageon the screen 606.

Next, FIG. 7 shows an example of starting an application program basedon the low-order four bits of the watermark. In this example, the tablefile contains the names of files used for executing applicationprograms. Numeral 703 indicates a window in which a reproduced image isdisplayed, and numeral 704 indicates a window in which an applicationprogram is displayed.

A personal computer 702 reproduces digital contents 701. In parallelwith this operation, the computer 702 extracts a watermark, compares thelow-order four bits of the watermark with the information described inthe table file 705 and, based on the comparison result, performs apredetermined operation. For example, when the low-order four bits ofthe watermark are [0000], the computer does not display data in thewindow 704. When the low-order four bits are [0001], the computerautomatically starts application program A and displays the result inthe window 704. When the low-order four bits are [0010], the computerstarts application program B and displays the result in the window 704.

Although the table file is used in the three examples described above,ASCII-coded data may be inserted directly into an image as a watermarkinstead of using the table file. In this case, when the watermark isdetected, a predetermined operation is executed. That is, character datacoded, for example, in ASCII code may be inserted directly into thelow-order four bits of a watermark. When the watermark is detected, thecharacter data is displayed, a web site is accessed automatically, or anapplication program is started.

Finally, a system to which the electronic watermark detection deviceaccording to the present invention is applied will be described.Compressed data generated when a watermark is inserted and a table fileare stored in a medium such as a DVD. They are distributed to an enduser as digital contents 401. In general, the digital contents 401 arereproduced on a reproduction device such as a DVD player or a personalcomputer. In the description below, an example of reproduction on apersonal computer will be described. A source filter 402 reads data fromthe digital contents 401. The data, once read, is split into video dataand audio data by an MPEG splitter 403. Video data, generated by thesplitting of the MPEG splitter 403, is decoded by a video decoder 405and is output to a video renderer 408. At this time, the video decoder405 outputs data, required for detecting a watermark, to a watermarkdetector 406. The watermark detector 406 detects a watermark based onthe data and passes the detected result to an application 404 via thevideo decoder. The detected watermark is 8-bit information 411. Theapplication 404 references the table file pre-stored in the digitalcontents and performs a predetermined operation as described above. Avideo renderer 408 performs processing for displaying decoded video dataand displays the video.

Although the watermark is 8 bits in length and the device uses thelow-order four bits of the eight bits in the above description, thewatermark may be n bits in length (for example, 16 bits, 32 bits, etc.)and the device may use m bits (m=<n). That is, the number of bits of awatermark does not matter.

The device according to the present invention allows a watermark to beused not only for copy protection but also for other purposes.Therefore, the device finds more applications in the system withouthaving to add major modifications to the conventional system.

1. A device that detects an electronic watermark from a compressedoriginal image, comprising: a circuit which reads said compressedoriginal image data, wherein the electronic watermark includesinformation consisting of first bits defined as CCI (copy protection)bits, second bits defined as reserved and third bits as undefinedbit-data; a circuit which decodes said compressed original image toproduce a decoded data; a circuit which performs inverse discrete cosinetransform (IDCT) for said decoded data; a circuit which detectselectronic watermark data embedded in data for which IDCT has beenperformed along with the value of said bit-data for which is defined aplurality of instructions; a table file including one of saidinstructions for said value of said bit-data; and a circuit whichperforms a processing according to said instruction in said table file.2. The device according to claim 1 wherein the electronic watermark datais eight-bit data and said bit-data is four-bit data in the low orderfour bits of said electronic watermark.
 3. The device according to claim1 wherein characters are displayed according to said instructioncorresponding to said bit-data.
 4. The device according to claim 1wherein a web site on the Internet is accessed according to saidinstruction corresponding to said bit-data.
 5. The device according toclaim 1 wherein an application program is started according to saidinstruction corresponding to said bit-data.
 6. A method for detecting anelectronic watermark from a compressed original image, comprising thesteps of: reading a compressed original image data, wherein theelectronic watermark includes information consisting of first bitsdefined as CCI (copy protection) bits, second bits defined as reservedand third bits as undefined bit-data; decoding said compressed originalimage data to produce a decoded data; performing inverse discrete cosinetransform (IDCT) for said decoded data obtained from said decoding step;detecting electronic watermark data embedded in data for which IDCT hasbeen performed, along with the value of said bit-data for which isdefined a plurality of instructions; and performing processing accordingto an instruction obtained from a table file including a plurality ofinstructions corresponding to values of said bit-data and which includesan instruction for said value of said bit-data.
 7. The method accordingto claim 6 wherein the electronic watermark is eight-bit data and saidbit-data is four-bit data in the low order four bits of said electronicwatermark.
 8. The method according to claim 6 wherein characters aredisplayed according to said instruction.
 9. The method according toclaim 6 wherein a web site on the Internet is accessed according to saidinstruction.
 10. The method according to claim 6 wherein an applicationprogram is started according to said instruction.
 11. Acomputer-readable recording medium storing therein a program fordetecting an electronic watermark embedded in an original image, saidprogram causing a computer to: read a compressed image data and a tabledata, said table data defining a plurality of instructions correspondingto said bit-data included in said electronic watermark, wherein saidelectronic watermark includes information consisting of first bitsdefined as CCI (copy protection) bits, second bits defined as reservedand third bits as undefined bit-data; decode said compressed image datain which said electronic watermark is embedded to obtain decoded data;perform inverse discrete cosine transform (IDCT) for decoded data;detect electronic watermark data embedded in data for which IDCT hasbeen performed; and perform processing according to one of saidinstructions in said table corresponding to said bit-data included insaid electronic watermark.
 12. A device that detects an electronicwatermark from an original image, from an original image, comprising: acircuit which reads said original image data; a circuit which detectssaid electronic watermark, wherein said electronic watermark includesinformation consisting of first bits defined as CCI (copy protection)bits, second bits defined as reserved and third bits as undefinedbit-data from said original image data along with the value of saidbit-data for which is defined one of a plurality of instructions; atable file including said plurality of said instructions correspondingto values of said bit-data; and a circuit which performs processingaccording to one of said instructions in said table file correspondingto the value of said bit-data contained in said original image.
 13. Thedevice according to claim 12 wherein the electronic watermark data iseight bit data and said bit-data is four bit data in the low order fourbits of said electronic watermark.